British and Irish Lions fly-half Finn Russell will join Bath from Top 14 side Racing 92 after the 2023 World Cup.
The Scotland playmaker is in his fifth season with the three-time Champions Cup finalists but will leave after the World Cup in France next October.
The 30-year-old, who joined Racing from Glasgow Warriors, has scored 272 points from 66 matches for the French side.
“To be able to join such a historic, well-supported club is really exciting,” Russell said.
“I know players at Bath who speak highly of the environment, and the direction the club is going in is something I want to be a part of.
“I’ve enjoyed my time at Racing 92 and I’ve learned a lot. Now is the right time for a new challenge, in a new league, with the aim of moving Bath back to the top end of the Premiership and competing for domestic and European titles.”
Russell, who made his Scotland debut in 2014 and has 65 caps, spent six years with the Warriors before moving to France.
He was part of the Lions team that toured New Zealand in 2017 as well as South Africa last year.
Russell was initially left out of the Scotland squad for this year’s autumn Tests, with head coach Gregor Townsend questioning his “form and consistency”.
But he was recalled for their match against New Zealand following an injury to Adam Hastings.
“Finn is a world-class player who will significantly add to our squad on and off the field,” Bath head of rugby Johann van Graan said.
“To be able to attract players of Finn’s quality to Bath Rugby is a credit to how far we have come as a club and a group since 11 July.”
Bath have signed a number of players since Van Graan took over this summer, with former Wasps forward Alfie Barbeary and ex-Worcester duo Ted Hill and Ollie Lawrence among those who have moved to the Recreation Ground.
However, fly-half Billy Searle has left the club after signing as short-term injury cover in October.
Chris Jones, BBC rugby union correspondent
Bath have tried and failed to land a big-name fly-half many times over the past decade, so this coup will be warmly received by their supporters, who are seeing the club build a formidable squad.
It’s also a boost for the Premiership after the league endured a brutal few months with the demise of Wasps and Worcester, with a number of high-profile players moving the other way to Russell as the salary cap cuts bite.
But Russell will be Bath’s marquee player, meaning his salary sits outside their cap, allowing him to be one of the highest-paid players in Premiership history.